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Pervious paving systems   
 Capital cost £/m2Net present value for 60 years £/m2Expected service life years
Porous asphalt: 30mm wearing course and 90mm base course25-3510610-20
Porous concrete: 150mm thick25-357930-60
Reinforced grass surface: 40mm high density polyethylene grid, 100mm root zone25-3511120-30
Concrete block pavers, 80mm, 50mm bedding40-5011230-40
Table notes %3Cbr /%3E%3Cbr /%3EA discount rate of 3% is used to calculate net present values. Costs are based on a type-A infiltration system and include pervious paving, 250mm MOT type 3 granular sub-base material and geotextile membrane. Infiltration tests, %3Cbr /%3Eexcavations and edgings are excluded. %3Cbr /%3E%3Cbr /%3ECosts-in-use include allowances for inspections, cleaning, relaying blocks, replacement of damaged surface, minor repairs, drainage and grass maintenance as applicable. Note that blocks and some of the sub-base material can be reused at the end of the service life after a rebuild of pavement so reducing life-cycle costs. No costs have been allowed for services excavations. %3Cbr /%3E%3Cbr /%3ECosts vary with the size of the project, extent and complexity of detailing, drainage design, bearing capacity of the soil and expected loads. Costs are influenced by the ability to use machinery rather then manual techniques. Costs are indicative and represent the average of a range. A cost analysis based on project specific information is essential for a realistic best value appraisal. BLP provides latent defect insurance for buildings (www.blpinsurance.com).